The present invention relates to an acoustic transformer for transmitting or receiving sound in a gaseous medium. In particular, this invention improves the performance characteristic of ultrasonic frequency electroacoustic transducers.
It is known that a directed ultrasonic beam can be produced by placing a conventional ultrasonic vibrator in the throat of a horn, as shown in U.S. Pat. No. 4,433,398. Such an ultrasonic transmitter is useful in ultrasonic speed sensing systems, such as described in U.S. application, Ser. No. 609,626 (E-12676), filed May 14, 1984 and assigned to the assignee of this application. For both velocity and distance measuring applications, it is desirable to have a transmitter which produces a narrow beam. For example, in Doppler velocity measurement, a wide transmit beam can cause a noisy reflected signal in that there will be a wide frequency variation in the reflected signals. Similarly, in distance sensing, a wide transmit beam can cause reflections from non-target objects. Therefore, a narrow beam ultrasonic transmitter is desired.